An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non- impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In this regard, "continuous" ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium.
In the case of "on demand" ink jet printers, at every orifice a pressurization actuator is used to produce the ink jet droplet. In this regard, either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators. With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. With respect to piezoelectric actuators, a piezoelectric material is used, which piezoelectric material possesses piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
Inks for high speed ink jet printers, whether of the "continuous" or "piezoelectric" type, must have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional spitting of ink droplets, the cavities and corresponding orifices are kept open. The addition of glycol facilitates free flow of ink through the ink jet chamber. Of course, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the orifices and may accumulate in the orifices and chambers themselves. That is, the ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. The particulate debris should be cleaned from the surface and orifice to restore proper droplet formation. In the prior art, this cleaning is commonly accomplished by brushing, wiping, spraying, vacuum suction, and/or spitting of ink through the orifice.
Thus, inks used in ink jet printers can be said to have the following problems: the inks tend to dry-out in and around the orifices resulting in clogging of the orifices; and the wiping of the orifice plate causes wear on plate and wiper, the wiper itself producing particles that clog the orifice.
Ink jet print head cleaners are known. An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled "Ink Jet Print Head Face Cleaner" issued Nov. 13, 1990, in the name of James C. Oswald. This patent discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and then out an outlet. A vacuum source is attached to the outlet to create a subatmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. Although the Oswald patent does not disclose use of brushes or wipers, the Oswald patent also does not reference use of a liquid solvent to remove the ink; rather, the Oswald technique uses heated air to remove the ink. However, use of heated air is less effective for cleaning than use of a liquid solvent. Also, use of heated air may damage fragile electronic circuitry that may be present on the print head face. Moreover, the Oswald apparatus does not appear to clean the print head face in a manner that leaves printing speed unaffected by the cleaning operation.
Another ink jet print head cleaner is disclosed in U.S. Pat. No. 4,600,928 by Braun et al. The patent teaches an ink jet printing apparatus which comprises an ultrasonic self cleaning system for cleaning of the print head assembly in which ink is supported in approximation to the orifices of the print head surface by means such as the capillary force. Ultrasonic cleaning pulses are then applied to clean the surface through fluid transmission of that ultrasound energy to said surface. However, this invention requires direct fluid communication between ink and the print head surface for cleaning purposes and it uses ink and not a more effective cleaning solvent for that purpose.
Another ink jet print head cleaner is disclosed in U.S. Pat. No. 5,574,485 by Anderson et al. Anderson patent teaches an ultrasonic liquid wiper for cleaning of a print head surface in which cleaning fluid is brought into close contact with the print head surface by the aid of a cleaning station. Ultrasonic energy in conjunction with the cleaning fluid are then used to dislodge dried ink particles from the print head surface, where they are removed using vacuum nozzles. However, this invention requires a relatively complex cleaning station including apparatus for scanning the liquid wiper across the print head surface.
Therefore, there is a need to provide a self-cleaning printer and method of assembling same, which self-cleaning printer provides effective cleaning without complex cleaning station apparatus.